llvm dev - Jan 2007 - [LLVMdev] ICmp documentation clarification

I just want to make sure I understand the semantic of the icmp function 
correctly as assumption are dangerous in this domain.

The syntax is specified as follow:
<result> = icmp <cond> <ty> <var1>, <var2>   ;
yields {bool}:result

But I can not find the documentation for <ty>. Is the following 
interpretation correct:
Both <var1> and <var2> are converted to <ty> using the
semantic of the trunc
instruction before processing the comparison operation.

Concerning instruction trunc, is bool considered to be an alias to type i1. 
If so, does the following stand true:
%Y = trunc i32 123 to bool               ; yields bool:true%Y = trunc i32 
122 to bool               ; yields bool:falseBaptiste.

Hi Baptiste,

On Fri, 2007-01-05 at 09:44 +0100, Baptiste Lepilleur
wrote:
> I just want to make sure I understand the semantic of the icmp function 
> correctly as assumption are dangerous in this domain.
> 
> The syntax is specified as follow:
> <result> = icmp <cond> <ty> <var1>, <var2>  
; yields {bool}:result
> 
> But I can not find the documentation for <ty>. 
<ty> is any of the integer types or a pointer type. It cannot be any
other type. The type of var1 and var2 must be identical and must be <ty>
> Is the following 
> interpretation correct:
> Both <var1> and <var2> are converted to <ty> using the
semantic of the trunc
> instruction before processing the comparison operation.
No, <var1> and <var2> are not converted or modified by this
instruction.
The values of the integers or pointers are compared, that's it.
> Concerning instruction trunc, is bool considered to be an alias to type i1.
Yes.
> If so, does the following stand true:
> %Y = trunc i32 123 to bool               ; yields bool:true
Yes. When you truncate to bool, it really truncates so only the least
significant bit is retained.
> %Y = trunc i32 122 to bool               ; yields bool:falseBaptiste. 
Yes.
> 
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Reid Spencer wrote:
> Hi Baptiste,
>
> On Fri, 2007-01-05 at 09:44 +0100, Baptiste Lepilleur wrote:
>> I just want to make sure I understand the semantic of the icmp
>> function correctly as assumption are dangerous in this domain.
>>
>> The syntax is specified as follow:
>> <result> = icmp <cond> <ty> <var1>,
<var2>   ; yields {bool}:result
>>
>> But I can not find the documentation for <ty>.
>
> <ty> is any of the integer types or a pointer type. It cannot be any
> other type. The type of var1 and var2 must be identical and must be
> <ty>
Thanks this clear things up.

What is the rational behind the existance of both icmp and fcmp as the i/f 
prefix seems to be redundant with <ty> ? Is it for performance purpose
when
analysing the code ?
>> [...]
> Yes. When you truncate to bool, it really truncates so only the least
> significant bit is retained.
>
>> %Y = trunc i32 122 to bool               ; yields bool:false
Maybe this example should be added to the doc to clarify this point.

Thanks,
Baptiste.